1. Field of the Invention
The present invention relates to a disc reproducing apparatus for reading information from an information recording disc.
2. Description of Background Information
ROM-type optical discs on which digital information has been recorded are generally classified into CLV (Constant Linear Velocity) discs and CAV (Constant Angular Velocity) discs, as two important disc types.
The CLV disc is advantageous from a viewpoint of a recording capacity because information is recorded at a uniform recording density irrespective of a radial position of the track. The CLV disc, however, requires that the disc must be rotated at a constant linear velocity. In the conventional CLV disc playing apparatus, therefore, a rotational speed of the disc is changed in accordance with the position of a pickup in the disc radial direction. This requires a rotation driving system having a complicated construction. Moreover, when accessing to a desired track, it takes a time period until a rotation servo is stabilized.
On the other hand, in case of a CAV disc, since information has been recorded on the disc at a constant rotational angular velocity, it is sufficient to control a rotation driving system of the disc at a constant rotational speed. The necessary construction is simple and it is possible to access to a desired track at high speed. A recording density, however, changes in accordance with the track radial position, namely, the recording density of tracks near the outer periphery is lower than that of tracks near the inner periphery, so that a recording capacity is smaller than that of the CLV disc.
The recording medium such as an ROM type optical disc is recently used to record or reproduce various kinds of information such as data, program, and the like as well as video images and audio data. An importance is paid to both of the high accessing speed and the long time reproduction (realization of a large capacity of recording information).